An arrangement of this kind is already known from VDI-Z 121 (1979) No. 3, pp. 83-95, particularly illustration 26. With respect to automation of production processes, arrangements of this type start with the fact that buffer zones must be provided between the transport means for the pallets and the production machines so as to be able to store pallets temporarily during unavailability of one or the other equipment.
The invention begins from this state of the art and has as its objective to fashion a manufacturing system in such manner that metal sheets can be fed to production machines automatically, without the need for essential modification of the latter.
The essence of the invention resides in the fact that a pallet storage for pallets loaded with stacks of sheet metal realized as a high (multi-tier) shelf is provided at a distance ahead of the feed station of the production machine, and that the intervening space is filled by a transport means which is guided along the pallet storage movably in the vertical and that the pallet storage is equipped with a pallet change arrangement as well as a single-part feeder for the automatic feeding of single sheets to the production machine.
High multi-tier shelves for the support of stacks of sheet metal carried by pallets are known. It is also known how to array transport means adjustable lengthwise and transversely as well as in elevation with such high multi-tier shelves. However, it is not known how to arry such tall multi-tier shelves, which in the case of the invention exhibit more of a columnar shape at a given distance ahead of a production machine, in order to take the pallets and/or stacks of sheet metal on the side away from the production machine and to place them into the high multi-tier shelf, while on the side facing the production machine the loaded pallets are removed from any tier of the high multi-tier shelf by the action of the transport means in the sense of the invention and brought into a position where the automatic feeding of single sheets to the production machine can take place.
A distinct advantage of the invention lies in the fact that the production machine need not be extensively modified in order to accomodate the production system.
In accordance with the invention, there is provided a single-item feed device having suction heads movably guided horizontally and vertically which acts upon the sheet metal surface. The feed device has the capability of always lifting the topmost sheet in the stack and feeding it to the production machine.
According to the invention, an important aspect lies in use of a transport means exhibiting on the side away from the production machine a support table for the metal sheets with elements which induce sliding, and whose support plane, in the transfer position of the transport means lies above the intake plane of the production machine. For the purpose of connection to said intake plane, the support table is capable of changing position. Thereto it is recommended that the support table for the sheet metal on the transport means is pivotable about an axis disposed above the intake plane, and is equipped with an oscillating drive. Thus the capability is attained of moving the metal sheet topmost at the moment along the sheet metal support table forward over such distance that upon slewing of said table a sliding movement of the metal sheet into the production machine can occur automatically because of gravity.
The particular problem of the invention resides in the capability to separate the several metal sheets of the sheet metal stack from one another. It is a fact that normally metal sheets are provided on their surfaces with a layer of grease, which increases the adhesion between the individual metal sheets significantly. In a stack of metal sheets thus treated, it would in principle be impossible to separate the topmost sheet from the one below it by a lifting motion alone.
The invention discloses therefore, in the framework of the overall principle of the invention, the arrangement of magnets on both sides close the stack near the corners facing the production machine. Magnet arrangement is such that positive and negative poles are held in a magnet holder at a distance one above the other and are turned towards the stack.
Such magnets can be realized as permanent magnets, or as switchable electro-magnets. If permanent magnets are used they must be adjustable from an inactive into an active position, particularly by pivoting. Switchable electro-magnets can remain in their position provided that the control permits activation of the magnets only during feed of single sheets.
The effect of the magnets emplaced and constructed in accordance with the invention lies in the fact that upon their excitation, steel sheets lying on top of one another tend to spread apart due to the magnetic flux. The magnetic excitation of the steel sheets therefore loosens the adhesive bond of the steel sheets in the area facing the production machine. As a consequence the steel sheets shift relative to one another in the direction of feed. Thus the topmost sheet moves furthest in rearward direction from the stack originally formed.
The invention utilizes this effect in such manner that the suction heads acting upon the sheet metal surface effect a downwards directed motion upon the rear area of the sheet metal before the forward motion for feeding the the metal sheet into the production machine takes place.
Thus this measure has the effect that the metal sheet lying topmost at any time is pressed downwards on its rearward side, while the forward side of the sheet is lifted due to the spreading action of the magnets. In this position, the topmost sheet can now be transferred without effort to the sheet support table of the transport means. As soon as the forward area of the topmost sheet lies upon said sheet support table, there is no longer any problem in advancing the sheet in the direction toward the production machine, and to then transfer it to the intake of said machine.
According to the invention, the suction heads are articulated. In order to accomplish this operation there is provide articulatedly journalled suction disks on the suction heads.
There are cases where cleaned or non-magnetizable sheets are stacked, so that the adhesion between individual sheets is reduced. Under such conditions the invention proposes that the suction heads acting upon the sheet surface be equipped with a vertically acting vibration drive. It has in fact become evident that under this repeated vertical impulse loading there takes place a loosening of the sheets from one another, i.e. a reduction of adhesion. One can thus control the motion components of such suction heads in series, in that repeated pressure and suction impulse is first imparted to the sheet topmost in the stack, and that then the sheet is moved in direction towards the production machine in raised position.
So as to prevent that two or more sheets are fed to the production machine together, the invention provides for a measuring means for sheet thickness in the transition area between the transport means and the production machine, where it is particularly recommended to implement said measuring means in form of an ultrasonic measuring instrument. Such a measuring instrument has the property of determining the difference in thickness of sheets, and even of measuring air spaces between layers of sheet metal.